Milling cutter

ABSTRACT

A rotary multi-tooth milling cutter, each tooth having a tooth face is provided. The tooth face has at least two sections, a first section nearest the cutting edge having a convex form as viewed in a cross section perpendicular to the cutter axis and a second section in a concave form.

This application is a continuing application of U.S. patent applicationSer. No. 09/273,468, filed on Mar. 22, 1999 now U.S. Pat. No. 7,186,063,which claims priority from Israeli Patent Application No. 123794, filedon Mar. 23, 1998.

FIELD OF THE INVENTION

The present invention relates to a Milling Cutter. More particularly,the invention provides a new and improved tooth form for such cutters,including end mills.

BACKGROUND OF THE INVENTION

Milling cutters are rotatable tools of cylindrical, conical, shaped ordisk form, having a plurality of cutting edges. Such cutters areavailable in many forms, such as plain cylindrical, side millingcutters, face and end mills, formed cutters, and standard and specialshaped profile cutters. High speed steel cutters are used for shortproduction runs, carbide cutters are often used for long runs. One formof a cutting insert is described by Satran in U.S. Pat. No. 5,685,670.Similarly for lathe tools, each cutting edge has a clearance angle whichis always positive, and a rake angle which is often positive, but may bezero or negative, for example when the cutter tooth is made of a hardgrade of tungsten carbide and machining is carried out at high speedsyet without a coolant. Also similar to lathe tools, the recommendedrelief angles and rake angles depend both on the material to be machinedand the material of which the cutter is made.

Much experimentation in the course of about a century has been carriedout in an effort to find the best tool tip angle for milling metals. Atool tip that has too small an included nose angle will fail todissipate heat and quickly reach temperatures causing softening and asharp reduction of operating life, and/or tool failure. Also, such atool is liable to vibrate, generate noise and may even break. Converselya tool tip having too large a cutting angle may fail to cut without theapplication of high cutting forces. Both too large and too small a toothtip angle can cause the production of a poor surface finish. Standardtextbooks, such as “TOOL ENGINEERS HANDBOOK” and “MACHINERY'S HANDBOOK”provide tables of recommendations for these angles, these being based onmuch experience and practical tests.

Much research has been carried out to determine the largest possiblevolume of metal removed before tool failure, in relation to a chosencutting speed. There are however so many additional factors involved,such as workpiece machinability rating, which itself is a function ofboth material type and heat treatment, tooth form, cutter size, numberof teeth and cutter material, machine tool power available at the cutterand machine tool rigidity, cutter rigidity, coolant type and flow rate,surface finish required, feed rate chosen, and depth and width of cutthat results published for one application are difficult to relate toother applications even where the basic type of work, e.g. milling, isthe same. It is however clear that tool tip heating Is detrimental tolong tool life, and anything that can be done to reduce the temperatureof the tool tip will bring its reward in increased tool life.

A type of cutter used extensively is, for example, the cylindrical highspeed steel and solid carbide end mill, which usually has helical teethand a tooth face having a rake angle in the range of for example 150degrees. The cutting face, as viewed in cross-section is usually asingle concave curve extending without break from the tooth root to thecutting edge. A disadvantage of this tooth form is that there occursextensive rubbing of the chip against the tooth rake face resulting inhigh power consumption, and the production of more heat than necessarywhich causes tool softening. It is of course the function of the liquidcoolant to remove such heat, but studies have shown that the coolantnever reaches the actual cutting edge which is most in need of cooling.In practice the coolant removes heat from the body of the tool and fromthe workplace, and heat is transferred by conduction from the hotcutting edge to the tool body. Tool steels are only moderately good heatconductors, so there is often a problem of too short a tool life due toa hot cutting edge.

A further problem is often encountered when using an end mill to machinea closed slot in ductile materials such as aluminum, copper, mild steeland brass in their annealed state. Chips do not clear easily out of thespace between the milling cutter teeth, despite the fact that, asopposed to lathe tools, milling cutters always produce discrete chips.The conventional tooth shape previously mentioned is not helpful withregard to chip clearance.

SUMMARY OF THE INVENTION

Bearing in mind this state of the art, it is now one of the objects ofthe present invention to effect an improvement in milling machinecutters, particularly end mills, and to provide a tooth form having astrengthened cutting edge and improved chip disposal.

The present invention achieves the above objects by providing a rotarymulti-tooth milling cutter, each tooth having a tooth face comprising ofat least two sections, a first section nearest the cutting edge having aconvex form as viewed in a cross section perpendicular to the cutteraxis.

In a preferred embodiment of the present invention there is provided amilling cutter wherein the length of said first section, as measuredsubstantially in the direction of the cutter center, comprises forexample 20% of the total length of the tooth face.

In a most preferred embodiment of the present invention there isprovided a milling cutter further provided with a concave chip-breakingsection located between said first and said second section.

Yet further embodiments of the invention will be described hereinafter.

In U.S. Pat. No. 5,049,009 there is described and claimed a rotarycutting end mill wherein the improvement claimed for the tooth formrelates to a first relief wall having an arcuate land segment and alinear land segment along a substantial portion of the cutting edge. Thearcuate land is located adjacent to the cutting edge and terminates at apoint along the first relief surface.

In contradistinction thereto, the present invention provides a convexsegment to form a face of the cutting edge.

It will thus be realized that the novel tooth form of the presentinvention serves to strengthen the tooth cutting edge, and is suitablefor cutting ferrous and non-ferrous metals. The convex form encourageschip disposal and produces an improved surface finish on the workpiece.

BRIEF DESCRIPTION OP THE DRAWINGS

The invention will now be described with reference to the accompanyingdrawings, which represent by example preferred embodiments of theinvention. Structural details are shown only as far as necessary for afundamental understanding thereof. The described examples, together withthe drawings, will make apparent to those skilled In the art how furtherforms of the invention may be realized.

In the Drawings:

FIG. 1 a is an elevational view of an end mill having a tooth formconstructed and operative according to a preferred embodiment of thepresent Invention;

FIG. 1 b is an enlarged cross-sectional view of a single tooth taken atAA in FIG. 1 a perpendicularly to the cutter axis;

FIG. 2 is a cross-sectional view of a tooth having preferredproportions;

FIG. 3 is a cross-sectional view of a tooth having a concave secondsection: and

FIG. 4 is a cross-sectional view of a tooth provided with a chipbreaker.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

There is seen in FIG. 1 a a rotary multi-tooth milling cutter 10. Thecutter 10 is an end mill, but the tooth form to be described isapplicable to various types of milling cutter.

FIG. 1 b shows one of the cutter teeth 12 of the same embodiment inenlarged form. The tooth 12 has a tooth face or cutting surfacecomprising of two sections, a first section 14 nearest the cutting edge16 having a convex form as viewed in a cross section perpendicular tothe cutter axis 18 in FIG. 1 a. The second section 20 is concave. Therake angle is indicated at “B” and the relief in angle at “C”. Cuttingedge path is indicated at “D” Referring now to FIG. 2, there is seen atooth 22 of a milling cutter, wherein the length of the first section24, as measured substantially in the direction of the cutter axis,comprises for example 20% of the total length of the tooth face.

The second section 26 is straight, and blends tangentially into thefirst section 24.

The following example illustrates the above relationships:

EXAMPLE 1

Type of cutter End mill Outside diameter 10 mm No. of teeth 4 Totaltooth depth 1.4 mm Length of first section 0.28 mm Length of secondsection 1.12 mm Shape of second section concave

FIG. 3 illustrates a tooth 28 of a milling cutter wherein the secondsection 30 is concave. Otherwise the tooth 28 is similar to that shownin FIG. 2. and numbered accordingly.

Seen in FIG. 4 is a tooth 30 of a milling cutter further provided with aconcave chip-breaking section 32. The chip-breaking section 32 islocated between the first 34 and the second section 36.

The scope of the described invention is intended to include allembodiments coming within the meaning of the following claims. Theforegoing examples illustrate useful forms of the invention, but are notto be considered as limiting its scope, as those skilled in the art willreadily be aware that additional variants and modifications of theinvention can be formulated without departing from the meaning of thefollowing claims.

1. A rotary, multi-tooth milling cutter having a central cutter axis,said milling cutter comprising: a plurality of teeth, each comprising alateral cutting edge being configured and disposed to be rotated aboutsaid central cutter axis and being configured to cut generally parallelthereto; said lateral cutting edge being configured and disposed to cutin a cutting direction along a circular cutting path centered at saidcentral cutting axis; said lateral cutting edge being configured anddisposed to define a non-zero relief angle disposed opposite saidcutting direction between said cutting tool and said cutting path; saidplurality of teeth each tooth comprising a first tooth face and a secondtooth face; said first tooth face comprising a surface, said first toothface surface being disposed to face away from the cutting direction;said second tooth face comprising a surface, said second tooth facesurface being disposed to face toward the cutting direction; said secondtooth face surface being disposed between said lateral cutting edge andsaid central cutter axis; said second tooth face surface comprising: atleast a first section and a second section being disposed between saidlateral cutting edge and said central cutter axis; said first section,being disposed to extend from said lateral cutting edge to said secondsection, comprising a continuously outwardly curved, convex shape beingconfigured and disposed to bulge outwardly in a direction towards thecutting direction; and said second section comprising a continuouslyinwardly curved, concave shape being configured and disposed to extendinwardly in a direction away from the cutting the direction.
 2. Themilling cutter as claimed in claim 1, wherein the length of the firstsection on the tooth face is 20% or less than the length of the toothface between the cutting edge and central cutter axis.
 3. The millingcutter as claimed in claim 1, wherein the first section blendstangentially into the second section.
 4. The milling cutter as claimedin claim 1, further including a concave chip-breaking section locatedbetween the first and second sections of the tooth face.
 5. The millingcutter as claimed in claim 1, wherein the first section is shorter inlength than the second section.
 6. The milling cutter as claimed inclaim 1, comprising one of: HSS, Solid Carbide, and Ceramics.
 7. Arotary, multi-tooth milling cutter having a central cutter axis, saidmilling cutter comprising: a plurality of teeth, each comprising alateral cutting edge being configured and disposed to be rotated aboutthe central cutter axis and being configured to cut generally parallelthereto; said lateral cutting edge being configured and disposed to cutin a cutting direction along a circular cutting path centered at saidcentral cutting axis; said plurality of teeth each comprising a firsttooth face and a second tooth face; said first tooth face comprising asurface, being disposed to face away from the cutting direction; saidsecond tooth face comprising a surface, being disposed to face towardthe cutting direction; said second tooth face surface being disposedbetween said lateral cutting edge and said central cutter axis; saidsecond tooth face surface comprising: at least a first section and asecond section being disposed between said lateral cutting edge and saidcentral cutter axis; said first section comprising an outwardly curved,convex shape being configured and disposed to bulge outwardly in adirection towards the cutting the direction; and said second sectioncomprising an inwardly curved, concave shape being configured anddisposed to extend inwardly in a direction away from the cutting thedirection.
 8. The milling cutter as claimed in claim 7, wherein saidfirst tooth surface being configured and disposed to define a non-zerorelief angle between said first tooth surface and said cutting path. 9.The milling cutter as claimed in claim 7, comprising one of: HSS, SolidCarbide, and Ceramic.
 10. A rotary, multi-tooth milling cutter having acentral cutter axis, said milling cutter comprising: a plurality ofteeth, each comprising a lateral cutting edge being configured anddisposed to be rotated about the central cutter axis and beingconfigured to cut generally parallel thereto; said lateral cutting edgebeing configured and disposed to cut in a cutting direction along acircular cutting path centered at said central cutting axis; saidplurality of teeth each comprising a first tooth face and a second toothface; said first tooth face comprising a surface being disposed to faceaway from the cutting direction; said second tooth face comprising asurface being disposed to face toward the cutting direction; said secondtooth face surface being disposed between said lateral cutting edge andsaid central cutter axis; said second tooth face surface comprising: atleast a first section and a second section being disposed between saidlateral cutting edge and said central cutter axis; said first section,being disposed to extend from said lateral cutting edge to said secondsection, comprising a continuously outwardly curved, convex shape beingconfigured and disposed to bulge outwardly in a direction towards thecutting direction; and said second section comprising a continuouslyinwardly curved, concave shape being configured and disposed to extendinwardly in a direction away from the cutting the direction.
 11. Themilling cutter as claimed in claim 10, wherein the length of the firstsection on the tooth face is 20% or less than the length of the toothface between the cutting edge and central cutter axis.
 12. The millingcutter as claimed in claim 11, wherein: the first section blendstangentially into the second section; and including a concavechip-breaking section located between the first and second sections ofthe tooth face.
 13. The milling cutter as claimed in claim 11, wherein:the meeting point of said first section and said concave section formingan angle; the first section is smaller in length than the secondsection; and said second section is concave.
 14. The milling cutter asclaimed in claim 11, comprising one of: HSS, Solid Carbide, and Ceramic.15. The milling cutter as claimed in claim 10, wherein the first sectionblends tangentially into the second section.
 16. The milling cutter asclaimed in claim 10, further including a concave chip-breaking sectionlocated between the first and second sections of the tooth face.
 17. Themilling cutter as claimed in claim 10, wherein the meeting point of saidfirst section and said concave section forming an angle.
 18. The millingcutter as claimed in claim 10, wherein the first section is smaller inlength than the second section.
 19. The milling cutter as claimed inclaim 10, wherein said second section is concave.
 20. The milling cutteras claimed in claim 10, comprising one of: HSS, Solid Carbide, andCeramic.